SEG 3300: Sections A&B Introduction to Software Engineering Lecture 1: Software and Software Engineering Based on Presentations LLOSENG (Lethbridge, Laganiere,2001, Williams 2001, Probert 2001)

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT The Nature of Software... Software is intangible Hard to understand development effort Software is easy to reproduce Cost is in its development —in other engineering products, manufacturing is the costly stage The industry is labor-intensive Hard to automate

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 3 The Nature of Software... Untrained people can hack something together Quality problems are hard to notice Software is easy to modify People make changes without fully understanding it Software does not ‘wear out’ It deteriorates by having its design changed: —erroneously, or —in ways that were not anticipated, thus making it complex

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 4 The Nature of Software Conclusions Much software has poor design and is getting worse Demand for software is high and rising We are in a perpetual ‘software crisis’ We have to learn to ‘engineer’ software

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 5 Types of Software... Custom For a specific customer Generic Sold on open market Often called —COTS (Commercial Off The Shelf) —Shrink-wrapped Embedded Built into hardware Hard to change

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 6 Types of Software Differences among custom, generic and embedded software

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 7 Types of Software Real time software E.g. control and monitoring systems Must react immediately Safety often a concern Data processing software Used to run businesses Accuracy and security of data are key Some software has both aspects

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT What is Software Engineering?... The process of solving customers’ problems by the systematic development and evolution of large, high- quality software systems within cost, time and other constraints Solving customers’ problems This is the goal of software engineering Sometimes the solution is to buy, not build Adding unnecessary features does not help solve the problem Software engineers must communicate effectively to identify and understand the problem

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 9 What is Software Engineering?… Systematic development and evolution An engineering process involves applying well understood techniques in a organized and disciplined way Many well-accepted practices have been formally standardized —e.g. by the IEEE or ISO Most development work is evolution Large, high quality software systems Software engineering techniques are needed because large systems cannot be completely understood by one person Teamwork and co-ordination are required Key challenge: Dividing up the work and ensuring that the parts of the system work properly together The end-product that is produced must be of sufficient quality

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 10 What is Software Engineering? Cost, time and other constraints Finite resources The benefit must outweigh the cost Others are competing to do the job cheaper and faster Inaccurate estimates of cost and time have caused many project failures

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Software Engineering and the Engineering Profession The term Software Engineering was coined in 1968 People began to realize that the principles of engineering should be applied to software development Engineering is a licensed profession In order to protect the public Engineers design artifacts following well accepted practices which involve the application of science, mathematics and economics Ethical practice is also a key tenet of the profession

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Stakeholders in Software Engineering 1. Users Those who use the software 2. Customers Those who pay for the software 3. Software developers 4. Development Managers All four roles can be fulfilled by the same person

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Software Quality... Usability Users can learn it and fast and get their job done easily Efficiency It doesn’t waste resources such as CPU time and memory Reliability It does what it is required to do without failing Maintainability It can be easily changed Reusability Its parts can be used in other projects, so reprogramming is not needed

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 14 Software Quality... QUALITY SOFTWARE Developer: easy to design; easy to maintain; easy to reuse its parts User: easy to learn; efficient to use; helps get work done Customer: solves problems at an acceptable cost in terms of money paid and resources used Development manager: sells more and pleases customers while costing less to develop and maintain

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 15 Software Quality The different qualities can conflict Increasing efficiency can reduce maintainability or reusability Increasing usability can reduce efficiency Setting objectives for quality is a key engineering activity You then design to meet the objectives Avoids ‘over-engineering’ which wastes money Optimizing is also sometimes necessary E.g. obtain the highest possible reliability using a fixed budget

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 16 Internal Quality Criteria These: Characterize aspects of the design of the software Have an effect on the external quality attributes E.g. —The amount of commenting of the code —The complexity of the code

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 17 Short Term Vs. Long Term Quality Short term: Does the software meet the customer’s immediate needs? Is it sufficiently efficient for the volume of data we have today? Long term: Maintainability Customer’s future needs

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Software Engineering Projects Most projects are evolutionary or maintenance projects, involving work on legacy systems Corrective projects: fixing defects Adaptive projects: changing the system in response to changes in —Operating system —Database —Rules and regulations Enhancement projects: adding new features for users Reengineering or perfective projects: changing the system internally so it is more maintainable

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 19 Software Engineering Projects ‘Green field’ projects New development The minority of projects

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 20 Software Engineering Projects Projects that involve building on a framework or a set of existing components. The framework is an application that is missing some important details. —E.g. Specific rules of this organization. Such projects: —Involve plugging together components that are: -Already developed. -Provide significant functionality. —Benefit from reusing reliable software. —Provide much of the same freedom to innovate found in green field development.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Activities Common to Software Projects... Requirements and specification Includes —Domain analysis —Defining the problem —Requirements gathering -Obtaining input from as many sources as possible —Requirements analysis -Organizing the information —Requirements specification -Writing detailed instructions about how the software should behave

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 22 Activities Common to Software Projects... Design Deciding how the requirements should be implemented, using the available technology Includes: —Systems engineering: Deciding what should be in hardware and what in software —Software architecture: Dividing the system into subsystems and deciding how the subsystems will interact —Detailed design of the internals of a subsystem —User interface design —Design of databases

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 23 Activities Common to Software Projects Modeling Creating representations of the domain or the software —Use case modeling —Structural modeling —Dynamic and behavioural modeling Programming Quality assurance Reviews and inspections Testing Deployment Managing the process

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT The Eight Themes of the Book 1. Understanding the customer and the user 2. Basing development on solid principles and reusable technology 3. Object orientation 4. Visual modeling using UML 5. Evaluation of alternatives 6. Iterative development 7. Communicating effectively using documentation 8. Risk management in all SE activities

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Difficulties and Risks in Software Engineering Complexity and large numbers of details Uncertainty about technology Uncertainty about requirements Uncertainty about software engineering skills Constant change Deterioration of software design Political risks

Managing the Software Process

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT What is Project Management? Project management encompasses all the activities needed to plan and execute a project: Deciding what needs to be done Estimating costs Ensuring there are suitable people to undertake the project Defining responsibilities Scheduling Making arrangements for the work continued...

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 28 What is Project Management? What is Project Management? Directing Being a technical leader Reviewing and approving decisions made by others Building morale and supporting staff Monitoring and controlling Co-ordinating the work with managers of other projects Reporting Continually striving to improve the process

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT Software Process Models Software process models are general approaches for organizing a project into activities. Help the project manager and his or her team to decide: —What work should be done; —In what sequence to perform the work. The models should be seen as aids to thinking, not rigid prescriptions of the way to do things. Each project ends up with its own unique plan.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 30 The opportunistic approach

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 31 The opportunistic approach … is what occurs when an organization does not follow good engineering practices. It does not acknowledge the importance of working out the requirements and the design before implementing a system. The design of software deteriorates faster if it is not well designed. Since there are no plans, there is nothing to aim towards. There is no explicit recognition of the need for systematic testing and other forms of quality assurance. The above problems make the cost of developing and maintaining software very high.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 32 The waterfall model V & V Requirements Gathering and Definition V & V Specification V & V Design V & V Implementation V & V Maintenance V & V Integration and Deployment

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 33 The waterfall model The classic way of looking at S.E. that accounts for the importance of requirements, design and quality assurance. The model suggests that software engineers should work in a series of stages. Before completing each stage, they should perform quality assurance (verification and validation). The waterfall model also recognizes, to a limited extent, that you sometimes have to step back to earlier stages.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 34 Limitations of the waterfall model The model implies that you should attempt to complete a given stage before moving on to the next stage —Does not account for the fact that requirements constantly change. —It also means that customers can not use anything until the entire system is complete. The model makes no allowances for prototyping. It implies that you can get the requirements right by simply writing them down and reviewing them. The model implies that once the product is finished, everything else is maintenance.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 35 The phased-release model V & V Requirements Gathering and Definition V & V Specification V & V Design V & V Implementation V & V Planning Phase 1 V & V Design V & V Implementation Phase 2 etc... V & V Integration and Deployment V & V Integration and Deployment

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 36 The phased-release model It introduces the notion of incremental development. After requirements gathering and planning, the project should be broken into separate subprojects, or phases. Each phase can be released to customers when ready. Parts of the system will be available earlier than when using a strict waterfall approach. However, it continues to suggest that all requirements be finalized at the start of development.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 37 The spiral model Requirements Specification Design Implementation Prototype Release 1 Release 2 Review Analysis of risk Integration and deployment

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 38 The spiral model It explicitly embraces prototyping and an iterative approach to software development. Start by developing a small prototype. Followed by a mini-waterfall process, primarily to gather requirements. Then, the first prototype is reviewed. In subsequent loops, the project team performs further requirements, design, implementation and review. The first thing to do before embarking on each new loop is risk analysis. Maintenance is simply a type of on-going development.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 39 The evolutionary model Time Development Activity

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 40 The evolutionary model It shows software development as a series of hills, each representing a separate loop of the spiral. Shows that loops, or releases, tend to overlap each other. Makes it clear that development work tends to reach a peak, at around the time of the deadline for completion. Shows that each prototype or release can take —different amounts of time to deliver; —differing amounts of effort.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 41 The concurrent engineering model

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 42 The concurrent engineering model It explicitly accounts for the divide and conquer principle. Each team works on its own component, typically following a spiral or evolutionary approach. There has to be some initial planning, and periodic integration.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 43 Choosing a process model From the waterfall model: —Incorporate the notion of stages. From the phased-release model: —Incorporate the notion of doing some initial high-level analysis, and then dividing the project into releases. From the spiral model: —Incorporate prototyping and risk analysis. From the evolutionary model: —Incorporate the notion of varying amounts of time and work, with overlapping releases. From the concurrent engineering: —Incorporate the notion of breaking the system down into components and developing them in parallel.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 44 Reengineering Periodically project managers should set aside some time to re-engineer part or all of the system The extent of this work can vary considerably: —Cleaning up the code to make it more readable. —Completely replacing a layer. —Re-factoring part of the design. In general, the objective of a re-engineering activity is to increase maintainability.

WINTER 2005 SEG 3300: SECTION A – R.L. PROBERT 45 Extreme programming Extreme Programming (XP) was created in response to problem domains whose requirements change. Your customers may not have a firm idea of what the system should do. You may not have to develop large requirement documents. Instead you write a series of about 80 user stories. Project planning is based on user stories. There must be a series of small and frequent releases; In many software environments dynamically changing requirements is the only constant. XP requires an extended development team. The XP team includes not only the developers, but the managers and customers as well You must be able to create automated unit and functional test